1. Field of the Invention
The invention relates to a liquid crystal compound, and more particularly to a liquid crystal compound with high color stability and a liquid crystal display comprising the compound.
2. Description of the Related Art
A reflective flexible display is the most important type of electronic display for next generation. The reflective flexible display utilizes plastic as a substrate material to replace traditional glass substrates, and has characteristics of being light, thin, and rugged etc. and may be made as roll-up displays for application as, for example, electronic tags, e-books, smart cards, flat panel displays, large billboards and tablet PCs etc.
A cholesteric phase can display various colors due to the selective reflection properties. In addition, its characteristic of bistability in a device can also make a screen “stay” like the display of a painting or a book without being applied voltage and can drive the cholesteric phase using voltage when switching of the screen is needed. This operation dramatically saves power consumption of a display and makes it much easier to carry and read. It is also one of the important trends for development of e-books.
In order to manufacture light-writing cholesteric liquid crystal displays, light-responsive chiral compounds having high helical twisting power (HTP) are needed. The molecular conformation of such compounds in liquid crystal is altered by illumination, resulting in an alteration of HTP and pitches of the cholesteric liquid crystals, which achieves an effect of changing colors of reflected light. Synthesis of a chiral dopant having a higher HTP value is desirable. When the chiral dopant is added to liquid crystals, the performance of the liquid crystals will not be lower and only a small amount thereof is needed to achieve the same twisting effect. Also, the problem of solubility will not be caused. A colorless light-responsive chiral compound is also required. Otherwise, a color light-responsive chiral compound will interfere with the wavelength of reflected light.
Therefore, when adding to liquid crystal formulation, light-responsive chiral compounds having the characteristics of a high HTP value, good solubility with liquid crystal formulation and being colorless etc. are required.